Unregistered First-Class Mail International items may be sealed at the sender’s option. Mailpieces not sealed by conventional means, such as moistening the gummed flaps on envelopes, must be closed in such a manner as to prevent the contents from falling out or being damaged during postal handling and transport. First–Class Mail International items that use Registered Mail service must be sealed. (See 334.4 for sealing requirements for Registered Mail service.)

Except as provided in 292.4 and 293.4, folded mailpieces, without envelopes, are admissible provided that all of the open sides are secured with tape, tabs, or wafer seals of sufficient quantity and strength to prevent the mailpieces from opening or being damaged during postal handling.